2,094 research outputs found
Infrared Observations of AGN
We present results from an imaging and spectroscopic study of the dust
properties of Seyfert galaxies in the 1-10um range. The data are compared to
state of the art models of torus emission to constrain geometrical and physical
properties of the obscuring medium.Comment: 2 pages, to appear in the IAU Symp.No.222 proceedings:"The Interplay
among Black Holes, Stars and ISM in Galactic Nuclei", Gramado, Brazil, March
1-5, 200
Type Iax Supernovae
Type Iax supernovae (SN Iax), also called SN 2002cx-like supernovae, are the
largest class of peculiar white dwarf (thermonuclear) supernovae, with over
fifty members known. SN Iax have lower ejecta velocity and lower luminosities,
and these parameters span a much wider range, than normal type Ia supernovae
(SN Ia). SN Iax are spectroscopically similar to some SN Ia near maximum light,
but are unique among all supernovae in their late-time spectra, which never
become fully nebular. SN Iax overwhelmingly occur in late-type host galaxies,
implying a relatively young population. The SN Iax 2012Z is the only white
dwarf supernova for which a pre-explosion progenitor system has been detected.
A variety of models have been proposed, but one leading scenario has emerged: a
type Iax supernova may be a pure-deflagration explosion of a carbon-oxygen (or
hybrid carbon-oxygen-neon) white dwarf, triggered by helium accretion to the
Chandrasekhar mass, that does not necessarily fully disrupt the star.Comment: Author version of a chapter in the 'Handbook of Supernovae', edited
by A. Alsabti and P. Murdin, Springer. 31 pages, 6 figure
The Morphology of Type Ia Supernovae Light Curves
We present a family of six BVI template light curves for SNe Ia for days -5
and +80, based on high-quality data gathered at CTIO. These templates display a
wide range of light curve morphologies, with initial decline rates of their B
light curves between m15(B)=0.87 mag and 1.93 mag. We use these templates to
study the general morphology of SNe Ia light curves. We find that several of
the main features of the BVI templates correlate tightly with m15(B). In
particular, the V light curves, which are probably a reasonably good
approximation of the bolometric light curves, display an orderly progression in
shapes between the most-luminous, slowest-declining events and the
least-luminous, fastest-declining SNe. This supports the idea that the observed
spectroscopic and photometric sequences of SNe Ia are due primarily to one
parameter. Nevertheless, SNe with very similar initial decline rates do show
significant differences in their light curve properties when examined in
detail, suggesting the influence of one or more secondary parameters.Comment: 32 pages, 15 figures, to appear in the Astronomical Journa
MarineTools.temporal: A Python package to simulate Earth and environmental time series
The assessment of the uncertainty about the evolution of complex processes usually requires different realizations consisting of multivariate temporal signals of environmental data. However, it is common to have only
one observational set. MarineTools.temporal is an open-source Python package for the non-stationary parametric
statistical analysis of vector random processes suitable for environmental and Earth modelling. It takes a single
timeseries of observations and allows the simulation of many time series with the same probabilistic behavior.
The software generalizes the use of piecewise and compound distributions with any number of arbitrary
continuous distributions. The code contains, among others, multi-model negative log-likely functions, wrappednormal distributions, and generalized Fourier timeseries expansion. Its programming philosophy significantly
improves the computing time and makes it compatible with future extensions of scipy.stats. We apply it to the
analysis of freshwater river discharge, water currents, and the simulation of ensemble projections of sea waves,
to show its capabilities
Galaxy Clusters in the Line of Sight to Background Quasars: I. Survey Design and Incidence of MgII Absorbers at Cluster Redshifts
We describe the first optical survey of absorption systems associated with
galaxy clusters at z= 0.3-0.9. We have cross-correlated SDSS DR3 quasars with
high-redshift cluster/group candidates from the Red-Sequence Cluster Survey. We
have found 442 quasar-cluster pairs for which the MgII doublet might be
detected at a transverse (physical) distance d<2 Mpc from the cluster centers.
To investigate the incidence (dN/dz) and equivalent-width distribution n(W) of
MgII systems at cluster redshifts, two statistical samples were drawn out of
these pairs: one made of high-resolution spectroscopic quasar observations (46
pairs), and one made of quasars used in MgII searches found in the literature
(375 pairs). The results are: (1) the population of strong MgII systems
(W_0>2.0 Ang.) near cluster redshifts shows a significant (>3 sigma)
overabundance (up to a factor of 15) when compared with the 'field' population;
(2) the overabundance is more evident at smaller distances (d<1 Mpc) than
larger distances (d<2 Mpc) from the cluster center; and, (3) the population of
weak MgII systems (W_0<0.3 Ang.) near cluster redshifts conform to the field
statistics. Unlike in the field, this dichotomy makes n(W) in clusters appear
flat and well fitted by a power-law in the entire W-range. A sub-sample of the
most massive clusters yields a stronger and still significant signal. Since
either the absorber number density or filling-factor/cross-section affects the
absorber statistics, an interesting possibility is that we have detected the
signature of truncated halos due to environmental effects. Thus, we argue that
the excess of strong systems is due to a population of absorbers in an
overdense galaxy environment, and the lack of weak systems to a different
population, that got destroyed in the cluster environment. (Abridged)Comment: Accepted for publication in the Astrophysical Journa
The Reddening-Free Decline Rate Versus Luminosity Relationship for Type Ia Supernovae
We develop a method for estimating the host galaxy dust extinction for type
Ia supernovae based on an observational coincidence first noted by Lira (1995),
who found that the B-V evolution during the period from 30-90 days after V
maximum is remarkably similar for all events, regardless of light curve shape.
This fact is used to calibrate the dependence of the B(max)-V(max) and
V(max)-I(max) colors on the light curve decline rate parameter delta-m15, which
can, in turn, be used to separately estimate the host galaxy extinction. Using
these methods to eliminate the effects of reddening, we reexamine the
functional form of the decline rate versus luminosity relationship and provide
an updated estimate of the Hubble constant of Ho = 63.3 +- 2.2(internal) +-
3.5(external) km/s/Mpc.Comment: 32 pages, 10 figures, AJ 1999 in pres
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